Centrifugal clutch with expansion ring assembly

ABSTRACT

A centrifugal clutch for utilization with an engine of a motorcycle is disclosed herein. The centrifugal clutch includes a clutch basket, a cover plate, a hub, first clutch plates, second clutch plates and a dynamic expansion ring assembly having cam members. The dynamic expansion ring assembly imparts substantially equal expansion forces in opposite directions. A gap is present when the engine is at an idle speed and cam members are positioned radially inward, and the gap is not present when the engine is operating faster than idle and the cam members are positioned radially outward by centrifugal force.

CROSS REFERENCE TO RELATED APPLICATION

The Present Application claims priority to U.S. Provisional PatentApplication No. 61/299,225, filed on Jan. 28, 2010, which is herebyincorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to centrifugal clutches for motorcycles,and a method and apparatus for converting a stock manufacturer manualclutch into a centrifugal clutch for a motorcycle.

2. Description of the Related Art

A typical motorcycle clutch includes a clutch basket, a hub, a cover andclutch plates. A typical motorcycle has two types of plates, a steelplate and a fiber plate (the fiber plate is usually constructed of analuminum substrate with a fiber material the substrate). A typicalmotorcycle clutch has eight fiber plates and seven steel platesstructured in an alternating manner with a steel plate positionedbetween each of the fiber plates. The fiber plates typically have twelvetabs that are positioned between fingers of a clutch basket which allowthe fiber plates to move with the clutch basket. Each of the steelplates has interior teeth that fit into a spline of an aluminum huballowing the steel plates to move with the aluminum hub. Each of thesteel plates preferably has a thickness of approximately 1.5 millimeters(“mm”) and each of the fiber plates typically has a thickness of 3 mm.The steel plates are 1.5 mm thick because the teeth are forced againstthe aluminum hub, which can groove quite easily due to the massiveamount of force. The exception to this general rule is a KTM rfs motor(no longer in production) which used 1 mm steel plates because the steelplates ran against a steel hub.

The clutch basket is connected to a crankshaft, and the hub is connectedto the transmission. The only connection between the engine and gear boxis the friction caused by the engagement of the fiber plates against thesteel plates, and the engagement comes from the force exerted bymultiple coil springs. The coil springs hold the engine and transmissiontogether at all times except when the clutch lever is pulled by a rider.When the clutch lever is pulled, a cam or slave is actuated whichcompresses the coil springs thereby creating gaps between the fiberplates and steel plates so that there is no longer any friction betweenthem. When the clutch lever is pulled, the engine and transmission aretwo completely separate entities. Usually the coil springs clamp ataround 200-300 pounds per square inch, which is more than enough toprevent the clutch from slipping. The clamping of coil spring feelspositive on the rider's hand, and if there is a shock load to thetransmission the clutch slips rather than breaking gears, sprockets orchains. For example, a shock load could come from a miscalculated jump.

Motorcycle clutches require the generation of sufficient centrifugalforce to clamp the clutch plates together without substantial slippageand without utilizing a larger sized case which exceeds the spaceallowances available in most motorcycles. In the past, a pressurecontrol mechanism was devised which combines the features of anautomatic clutch with the performance of a traditional manual clutch sothat the clutch engages smoothly without the use of a clutch lever atlow speeds but limits the actual force transmitted to the clutch platesby the cam members at higher speeds. At the same time, the pressurecontrol mechanism cooperates with a manual override lever to minimizethe hand pressure required to override the cam members and effectivelyoperate as a conventional manual clutch with relatively light feel ormanual pressure and yet be capable of operating within the same spacelimitations as the standard or stock motorcycle clutches. Further, withhydraulic actuated clutches, there is no way of adjusting the hydraulicfluid in order to act on a clutch pack.

The prior art discloses various clutch mechanisms for motorcycles. Oneexample is Youngwerth, Jr. et al., U.S. Patent Publication Number2009/0242351, for an Automatic Clutch employing Expanding Friction DiskAnd An Adjustable Pressure Plate, which discloses an expanding frictiondisk assembly that expands under centrifugal force to provide automaticengagement of the clutch.

Yet another example is Maimone, U.S. Pat. No. 6,533,056 for a MotorcycleAutomatic Clutch With Manual Release which discloses the use of arelease plate which is movable between a first and second position tomanually disengage the clutch.

Yet another example is Youngwerth, U.S. Pat. No. 6,957,730 for a ClutchApparatus With An Automatic Centrifugal Engagement Of Pressure Platewhich discloses a centrifugal pressure plate that moves axially whichcauses the plates to couple thereby forcing engagement between theengine and the transmission.

There is still a need for a mechanism to easily convert a standardmotorcycle clutch into a centrifugal clutch.

BRIEF SUMMARY OF THE INVENTION

The present invention is a novel improvement upon the clutch featuresdiscussed in U.S. Pat. Nos. 6,705,446, 6,814,208, 7,014,026 and7,140,480, which have been assigned to the assignee of the presentapplication and which are all herein incorporated by reference in theirentireties. The present invention allows a stock manufacturer manualclutch to be converted into a centrifugal clutch.

The main feature of the present invention is a dynamic expansion ringassembly. The dynamic expansion ring assembly preferably fits within astock motorcycle clutch allowing the stock manufacturer manual clutch tobe converted into a centrifugal clutch. In a preferred embodiment, thedynamic expansion ring assembly is substituted for a fiber clutch plate.The dynamic expansion ring assembly can be considered a fiber platesince fiber material is bonded on both sides of the dynamic expansionring assembly. In an alternative embodiment, one additional fiber plateis removed from a stock manufacturer manual clutch, however, the surfacearea of the fiber on the dynamic expansion ring assembly is on averagethat of 1.5 fiber plates. Since the steel plate and fiber platesalternate, losing one fiber plate means losing one steel plate. In thisembodiment, the steel plates are machined on one side to the size of theinside diameter of the fiber to create additional space for the dynamicexpansion ring assembly. The steel plates are machined down to 1 mm onlywhere the steel plate engages with a fiber plate so as to not change thecross-sectional area of the interior teeth of the steel plate thatengage the aluminum hub.

The dynamic expansion ring assembly contains ball bearings encompassedin multiple ramps. Six springs holding the two pieces of the dynamicexpansion ring assembly together and these springs change the speed atwhich the engine has to spin before the dynamic expansion ring assemblyopens.

The present invention allows a change from neutral to gear without usinga clutch lever and never stalling because there is a gap within theclutch pack (similar to when a rider pulls a clutch lever on a stockclutch). The gap is created by adjusting a clutch cable or hydraulicfluid of a hydraulic actuate clutch. The tighter the clutch cable (morepreload), the bigger the gap. With motorcycles that use a hydraulicclutch there is a slave that preloads the clutch springs. As soon as theengine increases speed above idle, the dynamic expansion ring assemblyexpands and closes the gap (in order for the dynamic expansion ringassembly to open, the force of the ball bearings must overcome the forceof the springs of the dynamic expansion ring assembly. The number ofsprings is 2, 3, 4 or 6). The faster the engine rotates, the greater theforce applied to the clutch pack. The maximum possible force that couldbe applied to the clutch pack is that of the stock coil springs(approximately 200-300 pounds per square inch (“psi”)). The gap that isrequired is approximately 0.025 inch. The dynamic expansion ringassembly can open up to 0.100 inch so after the gap closes there isapproximately 0.075 inch available (the extended opening of the dynamicexpansion ring assembly allows for wear) which would only open up if theforce was 200 psi, which only occurs at high rotations per minute(“RPM”).

The clutch lever remains and works at all times because the clutch leverhas overall more travel than the dynamic expansion ring assembly, so theclutch lever can open the gap at any engine speed similar to a stockclutch. The clutch lever feels positive on the rider's hand, and ifthere is a shock load to the transmission it will slip rather than breakgears, sprockets or chains, because the maximum force on the pack isapproximately 200-300 psi. In a hydraulic actuated clutch, an aspect ofthe invention is adjusting a reservoir cap on a master cylinder toadjust the gap.

The adjustment of the gap is performed externally, without tools in mostcases, by loosening of the clutch cable which allows for the return of astock clutch set up in order to bump start the bike.

In a preferred embodiment, the present invention is a centrifugal clutchwith a dynamic expansion ring assembly specifically adapted formotorcycles and which is preferably composed of a minimum number ofparts which can be retrofit into most standard centrifugal clutcheswhich employ annular clutch plates, commonly referred to as a “clutchpack”. The clutch pack is modified to incorporate a dynamic expansionring assembly at an intermediate location between the clutch plates, asopposed to being mounted at one end. If a manual override is utilized,the manual override employs a control rod to control a gap between oneend of the clutch elements and a spring-loaded cover plate to maintainthe clutch elements in the disengaged position at lower speeds as wellas enable shifting of the clutch out of clutching engagement at higherspeeds with a minimum degree of manual force required. Among otherfeatures is the ability to employ the dynamic expansion ring assembly inplace of one or more of the standard clutch plates without increasingthe total space occupied by the clutch pack, and eliminating a separatepressure plate within the cover at one end of the clutch pack whileachieving increased stability and control in engaging and disengagingthe multiple clutch plates in the clutch pack.

One aspect of the present invention is a centrifugal clutch forutilization with an engine of a motorcycle. The centrifugal clutchincludes a clutch basket, a cover plate, a hub, first clutch plates,second clutch plates and a dynamic expansion ring assembly. The clutchbasket includes a base plate with periphery walls spaced apart by teethengaging slots. The cover plate is mounted on the clutch basket. Thecover plate has an undermost portion. The hub has a cylindrical wallwith radial slots. The hub extends through a center of the clutchbasket. Each of the first clutch plates is positioned within the clutchbasket. Each of the first clutch plates has teeth for engaging with acorresponding teeth engaging slot of the teeth engaging slots of theclutch basket. Each of the first clutch plates comprises a non-metalmaterial. Each of the second clutch plates is positioned within theclutch basket. Each of the second clutch plates has radially inwardlyextending teeth. Each of the radially inwardly extending teeth engagewith a corresponding radial slot of the slots of the cylindrical wall ofthe hub. Each of the second clutch plates is composed of a metalmaterial. The dynamic expansion ring assembly is positionedsubstantially in a middle of the clutch basket. The dynamic expansionring comprises a first cam ring portion, a second cam ring portion andcam members held between the first cam ring portion and the second camring portion. The first cam ring portion comprises cam receivingportions, external teeth and cam faces. The second ring portioncomprises indented cam faces. Each of the external teeth engage with acorresponding teeth engaging slot of the teeth engaging slots of theclutch basket. The cam members are capable of moving inward and outwardin the each of the cam receiving portions. The dynamic expansion ringassembly imparts substantially equal expansion forces in oppositedirections away from the dynamic expansion ring assembly and against thefirst clutch plates and the second clutch plates to urge them intoclutching engagement. A gap is present between the cover plate and anend plate of the plurality of first clutch plates when the engine is atan idle speed and each of the cam members is positioned radially inwardin the dynamic expansion ring assembly. The gap is not present when theengine is operating faster than idle and each of the cam members ispositioned radially outward in the dynamic expansion ring assembly bycentrifugal force.

Having briefly described the present invention, the above and furtherobjects, features and advantages thereof will be recognized by thoseskilled in the pertinent art from the following detailed description ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view partially in section of one embodiment of a clutchmechanism and schematically illustrating a shift drum for regulating thegear ratio between a transmission shaft and motorcycle, kickstart lever,clutch lever, crankshaft driven off of an engine, and gear drive.

FIG. 2 is an exploded view of the clutch housing illustrated in FIG. 1.

FIG. 3 is a sectional view taken about lines 3-3 of FIG. 2.

FIG. 4 is another sectional view of the clutch housing with the engineat idle speed.

FIG. 4 a is a detailed view taken at 4 a of FIG. 4 and illustrating inmore detail a gap present at idle speed.

FIG. 5 is another cross-sectional view of the clutch housing showing therelationship between parts when a control rod is disengaged.

FIG. 5 a is a detailed view taken at circle 5 a of FIG. 5 andillustrating the relationship between parts when the engine is aboveidle speed.

FIG. 6 is a cutaway, enlarged view of the clutch housing.

FIG. 7 is an exploded view of the clutch plates and dynamic ringassembly as well as spring-loaded cover plate of the one embodiment.

FIG. 8 is an exploded view of the cam ring assembly of the oneembodiment.

FIG. 9 is a plan view of the cam ring assembly.

FIG. 10 is an exploded view in section through lines 10-10 of FIG. 9.

FIG. 11 is a plan view of one of the cam ring tracks of the assemblyshown in FIG. 9.

FIG. 12 is an enlarged cross-sectional view taken about lines 12-12 ofFIG. 11.

FIG. 13 is a plan view of another cam track of the cam ring assemblythat fits within the cam ring portion shown in FIGS. 9 to 12.

FIG. 14 is a cross-sectional view taken about lines 14-14 of FIG. 13.

FIG. 15 is a plan view of the inner surface of the cam track shown inFIG. 13.

FIG. 16 is an enlarged sectional view taken about lines 16-16 of FIG.15.

FIG. 17 is a plan view of a clutch plate.

FIG. 18 is a cross-sectional view taken about lines 18-18 of FIG. 17.

FIG. 19 is a plan view of a modified form of cam track of the cam ringassembly.

FIG. 20 is a cross-sectional view taken about lines 20-20 of FIG. 19.

FIG. 21 is a plan view of the modified form of cam ring assembly shownin FIGS. 19 and 20.

FIG. 22 is a cross-sectional view taken about lines 22-22 of FIG. 21.

FIG. 23 is an enlarged cross-sectional view taken about lines 23-23 ofFIG. 21.

FIG. 24 is a cross-sectional view taken about lines 24-24 of FIG. 21.

FIG. 25 is a plan view of the outer surface of the modified cam assemblyshown in FIG. 21.

FIG. 26 is a plan view of another cam track which fits into the cam ringportion illustrated in FIG. 21.

FIG. 27 is a cross-sectional view taken about lines 27-27 of FIG. 26.

FIG. 28 is a plan view of the inner surface of the cam portion shown inFIG. 26.

FIG. 29 is a cross-sectional view taken about lines 29-29 of FIG. 28.and

FIG. 30 is a cross-sectional view taken about lines 30-30 of FIG. 28.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of a centrifugal clutch is shown in FIGS. 1 to 19in which a clutch 10 is specifically adaptable for use in a motorcycle,not shown. As specifically shown in FIG. 1, a crankshaft C is driven byan engine, not shown, to impart rotation to a power input side of theclutch 10 via a gear drive N or other standard drive means. The geardrive N imparts rotation to a first sprocket S at one end of a clutchhousing H which is broadly made up of outer walls and base of a clutchbasket 12 and a cover plate 28 to be hereinafter described in moredetail. A transmission shaft 14 is secured at one end by a nut 15 withinthe clutch housing H and is rotated by a hub 16 within the clutchhousing H when the first plurality of clutch plates 18 and the secondplurality of clutch plates 20 are engaged by a dynamic expansion ringassembly 22; and through speed reduction gearing P, are operative torotate the standard drive means, not shown, off of an output sprocket S′to the rear wheel of the motorcycle. A shift drum D controls the gearratio of the gearing P, and a kickstart lever K operates in a well-knownmanner through gears L1, L2 and L3 through the crankshaft C to start theengine.

When a manual override is utilized, a control rod 26 extends into theclutch housing H in spaced inner concentric relation to the hollowtransmission shaft 14 and is manually controlled by a hand lever Ltypically mounted on the handle bar of the motorcycle and which operatesthrough a control cable A to force the cover plate 28 axially to form agap G between the cover plate 28 and an end plate of the first clutchplates 18 as shown in FIGS. 4 and 4A. When the clutch lever L issqueezed by the operator, the control rod 26 acts through the clutchplate lifter to lift the cover plate 28 for a distance greater than thedynamic expansion ring assembly 22 is capable of expanding and the gap Gis thereby created to disengage the drive irrespective of the speed ofthe motorcycle.

As shown in more detail in FIGS. 2 to 8, the clutch basket 12 includesan annular base plate 30 with upstanding circumferentially spacedperiphery walls 32 which are spaced apart to define teeth-engaging slots33 at uniformly spaced intervals. The periphery walls 32 are affixed toand extend upwardly from the outer periphery of the base plate 30, andinturned ledges 34 are located at the free ends of each of the peripherywalls 32. The clutch basket 12 is preferably of standard constructionand one example is a model manufactured by Kawasaki (Part No.13095-0052). A hub 16 is mounted within the hollow interior of theclutch housing H and includes a hollow cylindrical portion 37 extendingupwardly from an annular base plate 38 with a thrust bearing 31interposed between the base plate 30 and the lower end of thecylindrical portion 37. A base plate 38 is disposed in adjacent spacedrelation to and above the base plate 30 and terminates in an outercircular wall 39 in inner spaced concentric relation to the spaced walls32 of the clutch basket 12.

The plurality of first clutch plates 18 alternate in position with theplurality of second clutch plates 20 within the clutch basket 12. Eachof the plurality of first clutch plates 18 are keyed to the peripherywalls 32 of the clutch basket 12 by radially outwardly extending teeth42 to inter-engage with the teeth-engaging slots 33. Each of theplurality of second clutch plates 20 are keyed to the outer cylindricalportion 37 of the hub 16 by radially inwardly extending teeth 44 whichinter-fit with radial slots in the cylindrical wall 37 of the hub 16.Each of the plurality of second clutch plates 20 is preferably composedof a relatively hard metal such as steel. Each of the plurality of firstclutch plates 18 is preferably composed of a metal such as aluminum, andeach has a plurality of circumferentially spaced, generally rectangularfibrous friction pads R. Each rectangular fibrous friction pads R extendradially for the substantial extent of one of the opposed flat surfacesof each of the second clutch plates 20. However, the opposite surface ofeach of the plurality of second clutch plates 20 is flat and has a flushengagement with an annular surface portion of a corresponding pluralityof first clutch plate 18.

In one embodiment, the dynamic expansion ring assembly 22 is utilized toconvert a standard motorcycle manual clutch into a centrifugal clutch.Each of a plurality of first clutch plates 18 comprise fiber and each ofa plurality of second clutch plates 20 comprise steel. Preferably, thereare eight first clutch plates 18 and seven second clutch plates 20. Theplurality of first clutch plates 18 ride in the clutch basket 12 withcircumferentially spaced tabs 42 that fit between the fingers of theclutch basket 12. The plurality of second clutch plates 20 ride upon analuminum hub 16 and each of the plurality of second clutch plates 20 hasteeth that fit in a spline of the aluminum hub 16. The first clutchplates 18 and the second clutch plates 20 alternate with a second clutchplate 20 positioned between first clutch plates 18. Typically, each ofthe plurality of second clutch plates 20 has a thickness ofapproximately 1.5 mm and each of the plurality of first clutch plates 18has a thickness of approximately 3 mm. The dynamic expansion ringassembly 22 is preferably positioned in a center position of the clutchbasket 12, typically substituting for a first clutch plate 18 when astandard manual clutch is converted into a centrifugal clutch. Forexample, as shown in FIG. 7, a preferred structure has a first clutchplate 18, a second clutch plate 20, a first clutch plate 18, a secondclutch plate 20, a first clutch plate 18, a second clutch plate 20, thedynamic expansion ring assembly 22, a second clutch plate 20, a firstclutch plate 18, a second clutch plate 20, a first clutch plate 18, asecond clutch plate 20 and a first clutch plate 18. In this preferredstructure, the dynamic expansion ring assembly 22 imparts substantiallyequal force against an equal number of first clutch plates 18 and secondclutch plates 20 on each side of the dynamic expansion ring assembly 22.

As shown in FIGS. 4, 5, 6 and 7, the cover plate 28 is mounted on theclutch basket 12 and has a radially outer wall portion 52 overlaying thefirst clutch plates 18 and the second clutch plates 20 between theperiphery walls 32 of the clutch basket. The cover plate 28 also has aradially inner slightly raised solid circular wall portion 54 which issubstantially flat and is provided with a central bore to receive aclutch lifter in the form of a cap-like extension of a sleeve member 56to receive the end of the control rod 26. The cover plate 28 ispreferably of unitary construction, and as shown in FIGS. 5 and 6, aseries of circumferentially spaced sleeves 58 extend outwardly from theinner wall portion 54, with each sleeve 58 terminating at its inner endin a radially inwardly extending annular lip 59. A series of tubularposts 60 project upwardly from the base plate 38 of the hub 16, witheach of the tubular posts 60 preferably adapted for insertion of ashoulder bolt 62 and outer surrounding compression spring member 64.Specifically, each bolt 62 has an enlarged head 66, a shoulder portion67 and a reduced diameter threaded stem portion 68, the latter beingthreadedly connected into each tubular post 60 of the hub 16. In thisway, the shoulder 67 bears against the spring 64 which is insertedbetween each sleeve 58 and tubular post 60 with the opposite end of eachtubular post 60 bearing against an annular lip 59.

The compression springs 64 are mounted under compression concentricallybetween each shoulder 67 and lip 59 of each post 60 to control the gap Gbetween the flat undersurface of the annular portion 54 of the coverplate 28 and the endmost friction pad-covered surface 51 of an end plateof the first clutch plates 18 in facing relation to the annular portion52. Initially, the gap G is created by adjusting the clutch cablemechanism so that as the clutch cable is tightened, the control rod 26forces the cap-like extension of the sleeve through the central bore.The sleeve member is provided with an external shoulder and bearingagainst the cover plate 28 to increase the gap G by overcoming thespring force of the compression spring 64. Gap adjustment is furtherdiscussed in greater detail in connection with the operation of theclutch.

The dynamic expansion ring assembly 22 is explained in detail inrelation to FIGS. 7 to 10. The dynamic expansion ring assembly 22 ispreferably positioned in the clutch basket 12 intermediately between thefirst clutch plates 18 and the second clutch plates 20.

The dynamic expansion ring assembly 22 preferably comprises a relativelythick first cam ring portion 82 of a generally L-shaped cross-sectionalconfiguration defined by an outer peripheral circular band 83 and afirst cam-receiving portion 85 extending radially inwardly from one edgeof the outer peripheral circular band 83. The first cam ring portion 82also preferably has indented, circumferentially spaced cam faces 84 onan inner surface 84′ and a continuous friction pad layer F on an outerflat surface 85′ of the portion 85, as further shown in FIGS. 12-16. Theouter peripheral circular band 83 is disposed in surrounding relation tothe cam faces 84 and is provided with radially outwardly projectingexternal teeth 86 which correspond to and are aligned with the externalteeth 42 on the first clutch plates 18.

As shown in FIGS. 13 to 16, the dynamic expansion ring assembly 22 alsohas a second cam-receiving portion 90 having a series of indentedcircumferentially spaced cam faces 89 on an inner surface aligned inopposed facing relation to the cam faces 84. The second cam-receivingportion 90 is inset within the band 83 and secured to the first ringportion 85 by the screw members 92 as best seen in FIG. 10. Each camface 89 is relatively shallow and flat at W between opposed end surfacesV in comparison with the spherical and inclined surface portions X and Yof each cam face 89. Another continuous friction pad layer F is joinedto the outer surface 74 so that, as best seen in FIG. 7, the frictionpad layers F are in opposed facing relation to two of the second clutchplates 20 of the clutch basket 12. A series of three screw members 92are illustrated in FIGS. 8 and 9 and are disposed in equally spacedcircumferential relation around the ring assembly 22 but the number ofscrew members 92 may vary in number up to a total of six, as shown inFIGS. 8 and 9, depending upon the spring-loading required in resistingthe expansion force of the cam members 88. The cam members 88 are in theform of ball bearings, each cam member being sized to fit between eachpair of confronting cam faces 84 and 89 when the second cam-receivingportion 90 bears against the first cam-receiving portion 85 and, undercentrifugal force, the cams 88 will undergo a combination of sliding androlling movement from the deepest spherical portions X of each cam face84 radially outwardly along the inclined surface portions Y. Thedistance of travel of the cam members 88 is sufficient to compress theclutch plates together on opposite sides of the cam ring assembly 22 andforce the endmost plate 18 of the clutch pack into engagement with theundersurface portion 52 of the cover plate 28, and the opposite endplate 18 bearing against the base 38 of the hub 16, for example, asillustrated in FIGS. 5 and 5A.

The second cam-receiving portion 90 is normally urged against the firstcam-receiving portion 85 by the screw members 92 which are inserted incountersunk bores 91 in the cam-receiving portion 90, and a threaded end70 of each screw member 92 is threaded into an aligned threaded bore 94,the bores 93 being located at equally spaced circumferential intervalsbetween the cam faces 84. In this way, the screw members 92 arespring-loaded by the compression springs 93, and the spring tension maybe regulated to resist radial outward movement of the cam members 88 andexpansion of the second ring portion 90 away from the first portion 85until the clutch reaches a predetermined rotational speed. Mostimportantly, the dynamic expansion ring assembly 22 impartssubstantially equal expansion forces in opposite directions away fromthe dynamic expansion ring assembly 22 and against the clutch plates 18and 20 to urge them into clutching engagement. Briefly summarizing fromthe above, the spherical shape of the cam members 88 and mating faces 84and 89 minimizes the friction and reduces assembly drag whilecontributing to a more responsive clutch feel. The position of thedynamic expansion ring assembly 22 in the middle of the clutch basket 12places the expansion forces closer to the center of mass for themotorcycle clutch and minimizes the likelihood of unbalanced forcesotherwise generated in models that are assembled with a pressure platebetween one end of a clutch pack and a cover. Further, to minimize wearof the first clutch plates 18 (which comprise fiber), the position ofthe dynamic expansion ring assembly 22 in the middle of the clutchbasket 12 evenly distributes the clutch expansion forces and providesfor more uniform disk pack compression. In one embodiment, in order tocompensate for the increase in thickness of the dynamic expansion ringassembly 22 which is substituted for a first clutch plate 18, theremaining first clutch plates 18 are machined to their thickness withoutaltering the effectiveness of the clutch pack. This is achieved with aminimum retrofit and substantially no modifications required to thestock original equipment manufacturer (“OEM”) parts since the dynamicexpansion ring assembly 22 is conformable to the existing OEM clutchpack. Further, utilizing the OEM clutch springs 64 and housing mechanismensures maximum ease of installation and adjustment for use in thefield.

As described in U.S. Pat. No. 7,014,026, assigned to the assignee of thepresent application, an important characteristic of the specialcompression springs 93 is their greatly reduced height or travel for agiven amount of resistance and can therefore occupy much less space inan axial direction. Preferably, the springs 93 are SPIRA WAVE® wavesprings which are flat wire compression springs manufactured and sold bySmalley Steel Ring Co. of Lake Zurich, Ill. Their spring force is suchas to resist the spreading of the cam portions 82 and 90 and provides amethod to increase or decrease spring force which in turn allows therider/operator to easily “fine-tune” the clutch engagement.

The maximum clamping force that can be exerted on the first clutchplates 18 and the second clutch plates 20 to assure non-slippingengagement under normal operating conditions is determined by the stocksprings 64 of the cover plate 28. The springs 64 permit the clutch toslip in the event that extreme shock loads are transmitted through thedrive train. For example, the first clutch plates 18 and the secondclutch plates 20 permit some slippage so as to absorb any shock loadingwhen the rear wheel of the motorcycle is off the ground and spinning,and then suddenly stops.

At engine idle, the cover plate 28 normally rides upon the clutch lifter55 thereby creating the gap G which is finely adjustable (larger andsmaller) with the OEM or standard clutch cable adjusters provided withthe clutch lever mechanism. The gap G can be reduced to zero in order toreturn to a stock clutch set up, this might be desirable in order to“bump” start the engine. Further, as the engine is idling the dynamicexpansion ring assembly 22 is in the relaxed position and the spacingbetween the first clutch plates 18 and second clutch plates 20 ispresent. As soon as the engine revs higher than idle the dynamicexpansion ring assembly 22 expands so that the gap G will close at theend of the clutch basket 12 and the first clutch plates 18 and thesecond clutch plates 20 move into positive engagement with one another.

In one alternative embodiment, the dynamic expansion ring assembly 22fits within a stock clutch basket and takes the place of one fiber plateso as to be within the size limits of the standard clutch housings. Thedynamic expansion ring assembly 22 can be considered a fiber plate as ithas the fiber material bonded on both sides. As space is an issue, oneadditional fiber plate is removed, however, the surface area of thefiber on the dynamic expansion ring assembly 22 is on average that of1.5 clutch plates. As you lose one fiber plate you also lose one steelplate. In order to provide additional space, the steel plates aremachined on one side to the size of the inside diameter of the fiber.

In another aspect of the present invention, a method for converting astandard manufacturer manual clutch into a centrifugal clutch beginswith positioning a dynamic expansion ring assembly 22 into a clutchbasket 12 as a substitute for a first clutch plate 18 comprising fiber.Next, a gap G is set by changing a tension in a clutch cable whereinloosening a cable tension by lengthening the clutch cable results in theincreasing of the gap G. Similarly, shortening the length of the clutchcable decreases the gap G and results in the first clutch plates 18 andthe second clutch plates 20 in contact with each other therebypermitting a bump start by “popping of the clutch.”

A modified form of dynamic expansion ring assembly 22′ is illustrated inFIGS. 19 to 30 wherein like parts are correspondingly enumerated withprime numbers. The modified form comprises multiple staggered rows ofcam faces 95 and 96 for cam members 88′ and 98 in the cam-receivingportion 85′; and cam faces 97 and 98 for the cam-receiving portion 90;however, the indented inner radial row 96 of cam faces are shorter onlyto accommodate a series of smaller cam members or balls 98 and in thisrelation, two or more staggered concentric rows of ball bearings areemployed as set forth and described in U.S. Pat. No. 7,140,480, assignedto the assignee of this application.

In use, one or more adjustments may be made in the dynamic expansionring assembly 22 or 22′ including but not limited to changing the numberof cam members in a single row, reducing the spring tension of thesprings 93 or changing the number of spring-loaded screw members 92 inregulating the resistance to expansion of the dynamic expansion ringassembly 22. If the number of the spring-loaded screw members 92 isvaried it is still important that they be symmetrically spaced about thedynamic expansion ring assembly 22 and apply equal tension or resistanceto expansion. When the dynamic expansion ring assembly 22 is expanded inresponse to displacement of the cam members 88 to lock the first clutchplates 18 and the second clutch plates 20 together, the hub 16 thenimparts the rotation of the clutch housing H to the transmission shaft14. The spring force of the spring-loaded screw members 92 is such as toresist spreading of the dynamic expansion ring assembly 22 beyond apre-determined limit which is the maximum pumping force that can besafely exerted on the first clutch plates 18 and the second clutchplates 20 to assure a non-slipping engagement but which will permit theclutch plates 18 and 20 to slip in the event that extreme shock loadsare transmitted through the drive train. In order to override theautomatic clutch, the control rod 26 is operated by the manual clutchlever L to advance against the clutch lifter and cover plate 28 to forma sufficient clearance space or gap G between cover plate 28 and the endplate of the first clutch plates 18.

In another embodiment, a hydraulic actuated clutch is utilized topreload the gap G of the clutch 10. The hydraulic actuated clutchcomprises a master cylinder that has a body substituted for a stockreservoir cap. The body is bolted to the master cylinder of thehydraulic system. The body preferably has a flat portion for attached tothe master cylinder with a cylindrical portion extending upward from theflat portion and having an aperture. A piston is positioned within theaperture of the cylindrical portion of the body. When the piston ispushed downward within the aperture, fluid is forced through a hydraulicline of the hydraulic system thereby creating a gap G in clutch 10, asdescribed above in relation to the clutch lever. A cap is placed overthe cylindrical portion of the body. The cap preferably threadinglyengages the cylindrical portion of the body. The tightening andloosening of the cap on the cylindrical portion adjusts the gap G in theclutch 10. Tightening the cap increases the size of the gap G, andloosening the cap reduces the size of the gap G. With the hydraulicadjuster arrangement, the gap G is controlled from a zero gap size to aninstalled gap G size. At a zero gap it is possible to bump start themotorcycle whereas the installed gap G operates as an automatic clutch.

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this invention andwill readily understand that while the present invention has beendescribed in association with a preferred embodiment thereof, and otherembodiments illustrated in the accompanying drawings, numerous changesmodification and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this invention which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claim. Therefore, the embodiments of the invention inwhich an exclusive property or privilege is claimed are defined in thefollowing appended claim.

1. A centrifugal clutch for utilization with an engine of a motorcycle,the centrifugal clutch comprising: a clutch basket comprising a baseplate with a plurality of periphery walls spaced apart by a plurality ofteeth engaging slots; a cover plate mounted on the clutch basket, thecover plate having an undermost portion; a hub having a cylindrical wallwith a plurality of radial slots, the hub extending through a center ofthe clutch basket; a plurality of first clutch plates positioned withinthe clutch basket, each of the plurality of first clutch plates having aplurality of teeth for engaging with a corresponding teeth engaging slotof the plurality of teeth engaging slots of the clutch basket, each ofthe plurality of first clutch plates comprising a non-metal material; aplurality of second clutch plates positioned within the clutch basket,each of the plurality second clutch plates having a plurality ofradially inwardly extending teeth, each of the plurality of radiallyinwardly extending teeth engaging with a corresponding radial slot ofthe plurality of slots of the cylindrical wall of the hub, each of theplurality of second clutch plates composed of a metal material; and adynamic expansion ring assembly positioned substantially in a middle ofthe clutch basket, the dynamic expansion ring comprising a first camring portion, a second cam ring portion and a plurality of cam membersheld between the first cam ring portion and the second cam ring portion,the first cam ring portion comprising a plurality of cam receivingportions, a plurality of external teeth and a plurality of cam faces,the second ring portion comprising a plurality of indented cam faces,wherein each of the plurality of external teeth engage with acorresponding teeth engaging slot of the plurality of teeth engagingslots of the clutch basket, wherein the plurality of cam members arecapable of moving inward and outward in the each of the plurality of camreceiving portions; wherein the dynamic expansion ring assembly impartssubstantially equal expansion forces in opposite directions away fromthe dynamic expansion ring assembly and against the plurality of firstclutch plates and the plurality of second clutch plates to urge intoclutching engagement; wherein a gap is present between the cover plateand an end plate of the plurality of first clutch plates when the engineis at an idle speed and each of the plurality of cam members ispositioned radially inward in the dynamic expansion ring assembly, andthe gap is not present when the engine is operating faster than idle andeach of the plurality of cam members is positioned radially outward inthe dynamic expansion ring assembly by centrifugal force.